Elixir's implementation of Fowler's Money pattern: https://martinfowler.com/eaaCatalog/money.html
Defines a Money struct that store the value and have methods to manipulate it.
The value is stored in the currency's sub_unit. e.g. "SLE 1" is stored as "100 cent".
Cases where arithmetic operations produce a floating number, the banker's rounding algorithm
is used to round to the nearest integer: https://rounding.to/understanding-the-bankers-rounding
Well, Erlangers know; it's Elixir with Erlang style naming, the erl prefix.